Samsung Electronics' Galaxy S3 surpassed the iPhone 4S as the top-selling U.S. smartphone in August, the first time that Apple's flagship phone has relinquished its position atop the smartphone food chain.

That's according to Canaccord Genuity analyst T. Michael Walkley, who checks in with retailers to see how each phone is doing.

The iPhone 4S, which initially launched with AT&T, Verizon Wireless, and Sprint Nextel, and then expanded to a number of other carriers, has held the top spot as the single best-selling phone ever since it launched in October. To have held on to that spot would have been impressive for any device, but has been par for the course for previous iPhones.